[WIP] Cotrending and stitching tutorials

[amcody]

Use this one instead of any previous pull request.

[codecov]

Codecov Report

Merging #67 into master will increase coverage by 5.87%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master      #67      +/-   ##
==========================================
+ Coverage   12.97%   18.84%   +5.87%     
==========================================
  Files          48       53       +5     
  Lines        9295     9466     +171     
==========================================
+ Hits         1206     1784     +578     
+ Misses       8089     7682     -407

Impacted Files	Coverage Δ
pyke/kephead.py	14.54% <0%> (-0.84%)	⬇️
pyke/kepdraw.py	6.71% <0%> (-0.81%)	⬇️
pyke/keptimefix.py	11.59% <0%> (-0.53%)	⬇️
pyke/kepft.py	10.22% <0%> (-0.37%)	⬇️
pyke/kepwindow.py	8.16% <0%> (-0.26%)	⬇️
pyke/kepclip.py	7.56% <0%> (-0.2%)	⬇️
pyke/kepbls.py	76.6% <0%> (-0.18%)	⬇️
pyke/kepdynamic.py	7.35% <0%> (-0.17%)	⬇️
pyke/kepfilter.py	6.15% <0%> (-0.15%)	⬇️
pyke/kepextract.py	79.15% <0%> (-0.11%)	⬇️
... and 34 more

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[mirca]

That's really cool! Thanks @amcody!

[barentsen]

Make sure to have a look at "Example 3" i.e. "Appendix D" in http://adsabs.harvard.edu/abs/2012PASP..124..963K -- it offers a more verbose version of this tutorial. We may want to borrow words from there.